The invention relates to the use of alkanesulfonic acids for increasing the permeability of underground, carbonatic mineral oil- and/or natural gas-carrying rock formations and for dissolving carbonatic and/or carbonate-containing impurities in mineral oil production, in particular at a temperature of at least 100° C.
In mineral oil or natural gas recovery, mineral oil- and/or natural gas-carrying rock formations are drilled. Typical rock formations comprise sandstone formations and/or carbonate formations. In the case of sandstone formations, the quartz particles are caked together by other materials, including carbonates. Of course, carbonatic formations, too, may have a certain quartz content or silicate content.
Owing to the difference between the pressure in the formation and the pressure in the well, the mineral oil or natural gas flows through fine channels, pores or the like in the formation to the well and is conveyed from there to the surface. The pressure in the formation may be of natural origin or may be artificially maintained, for example, by forcing in water, steam or other liquid or gaseous media through an injection well.
In order to ensure an economical production rate for mineral oil and natural gas, the porosity of the rock formation must reach a certain degree. Frequently, however, the porosity of the rock formation is too low. On the one hand, the natural porosity may already be too low; on the other hand, however, pores which are sufficiently large per se may become blocked with particles, for example rock particles, in the course of time. It is therefore known that the rock formation can be hydraulically disintegrated for creating pores and channels (also referred to as “fracturing treatment” or “fracturing”).
Blockages may form in particular through CaCO3 or BaCO3. In the rock formation, a higher concentration of calcium carbonate is dissolved in the formation water under the naturally occurring conditions (high pressure, high temperature) than under normal conditions (1 bar, room temperature). If formation water saturated with CaCO3 enters zones of low temperature and/or relatively low pressure, the CaCO3 or BaCO3 crystallizes out. This is the case, for example, in the vicinity of the production well. As a result, the porosity of the formation is reduced.
Furthermore, the formation water cools on the way to the Earth's surface, with a result that CaCO3 deposits or BaCO3 deposits also form in the well itself. Also as a result of this, the productivity of oil or gas production is reduced.
It is known that such blockages in the well or in the formation can be eliminated by an acid treatment (also referred to as “acidizing treatment” or “acidizing”). Furthermore, new channels or pores can also be created in the formation by an acidizing treatment. Further details in this context are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 6th Edt., 2000 Electronic Release, “Resources of Oil and Gas, 3.4.2. General Production Engineering”.
For example, aqueous solutions of HF and/or HCl are used as acids for the acidizing treatment. HF is of course suitable here for silicate formations, and HCl is used in particular for carbonatic formations. However, the use of organic acids has also been disclosed.
US 2005/16731 discloses a method for dissolving silicate material in a sandstone formation of a mineral oil deposit, in which a buffered solution of an organic acid is first forced into the formation and a solution comprising HF is forced in only in a second step. The organic acid may be, for example, formic acid, acetic acid or citric acid.
US 2004/9880 discloses a mixture for the treatment of sandstone formations which comprises water, an acid-hydrolyzable surface-active substance, an inorganic acid, for example HCl, and an organic acid. The inorganic acid may be, for example, hydrochloric acid, sulfuric acid or nitric acid, and the organic acid may be, for example, formic acid, acetic acid, citric acid or methanesulfonic acid. The treatment of carbonatic rock formations is not disclosed.
Owing to the high vapor pressure, HCl is not suitable for use at relatively high temperatures. Moreover, HCl is highly corrosive, particularly at relatively high temperatures.
U.S. Pat. No. 6,805,198 discloses a method for increasing the permeability of underground rock formations at relatively high temperatures, in particular from 92° C. to 204° C., with the use of organic dicarboxylic acids, such as, for example, oxalic acid, malonic acid or adipic acids. However, formation of undesired precipitates, for example of calcium oxalate, may occur here. Furthermore, relatively large amounts of the comparatively weak acids are required.
WO 95/14641 discloses alkanesulfonic acids, optionally as a mixture with other acids, such as, for example, amidosulfonic acid, for removing lime deposits, in particular in the household.